Electronic shelf labels are beginning replacing paper shelf labels in supermarkets. For each product placed on a shelf, a modern electronic label can display both information for consumers (price, unit price, promotion . . . ) and information for employees of the store (inventory, facing, barcode . . . ).
Generally, electronic labels are wirelessly connected to a main server located somewhere in the store, in which data about all products is managed. This server is traditionally connected to the store back office, in order to be gather all information required to display on the ESL. Several radio technologies are commonly used, including WiFi, radio waves or infrared transmission.
The information displayed by the labels is regularly updated. Prices may evolve, configuration of shelves may change. To this end, protocols of transmission are used to send messages from the server to the targeted labels.
Existing protocols generally meet all the expectations for supermarkets and hypermarkets in which the electronic shelf labels use Segmented Display technology. However when graphic display technology, i.e. a 2-dimensional array of lit or unlit pixels (also named “DotMatrix Display” technology) is used, existing protocols require some advanced compression techniques to meet customer expectations in terms of throughput and ESL update rate.
The number of electronic labels commonly reach tens of thousands in hypermarkets. At this scale, bandwidth and throughput can become bottlenecks. The amount of data to be sent at each update may indeed overpass wireless capability. Gaps of several minutes may then appear between the launching of an update by the server and the effective display update of the labels, which could mislead customers and generate errors, if shifts occur between displayed prices and real prices.
Moreover, electronic shelf labels are commonly battery powered and each data transmission draws energy. As electronic labels only comprise a small embedded battery whose lifetime is long but limited, the increase of the amount of data to be transferred directly shorten the life expectancy of labels.
These problems will still increase in coming years, as new labels are expected, these labels being provided with large high-resolution LCD screens, or even with color displays.
A first solution to this problem is to directly send raw data to the labels. These data are less voluminous, but have to be processed by the label itself for being displayed. It requires complex labels comprising an improved treatment unit, and possibly a memory. These labels are more expensive, and above all consume more energy, which is not acceptable as electronic labels only comprise an embedded small battery whose lifetime is long but limited.
International patent application WO03/073261 proposes a method for lowering the energy consumption when updating the display with new product information. The idea is to update only the part of the display which has to be updated. Messages are sent in coded text, and displays are derived from this text and from fonts stored in each label.
However, if this method reduces the problem, it does not solve it. Indeed, the needed bandwidth remains proportional to the number of labels in the supermarket. Besides, labels require enough memory for storing every font of the store in every size.